Traveling to Mars is no simple feat, and it's much more difficult than a relatively short trip to the moon. The atmosphere on Mars is thinner than the Earth's, so it poses a significant threat to any vehicle that attempts to land on the planet. Plus, a trip to Mars could take months depending on how much fuel is used (or what kind of propulsion is used). Still, several projects are making the ambitious journey, and here are just a few examples of Martian missions.
If you'd like to read more awesome and interesting stuff, check out this unrelated (but not entirely random!) Techdirt post